As is known, a method referred to as autocollimation serves firstly to determine an inclination of an autocollimation target and secondly to determine an orientation of the autocollimation target. The term inclination usually denotes a deviation of a vertical angle from a desired position, while the term orientation denotes a deviation of a horizontal angle from the desired position.
A plane mirror is usually used as an autocollimation target, said mirror being fitted to an object whose inclination and orientation are to be determined. The object can be e.g. components which are to be connected exactly to other components in a production plant. One example is motor vehicle doors, which, in a production plant, have to be aligned very precisely for incorporation in a motor vehicle body, in order to be able to be fitted in exactly, without stoppages of the assembly line occurring.
A second purpose of an autocollimation process is to produce an optical reference line that is perpendicular to the autocollimation target. In this case, it is necessary, instead of the target itself, to set up the telescope used for autocollimation such that the optical axis of said telescope is precisely perpendicular to the autocollimation target.
Hitherto, such an autocollimation has been carried out manually. For this purpose, a telescope, the construction of which can be seen schematically from FIG. 1, is aligned in the direction of the autocollimation target. Next, the telescope is set to “infinity” by a displacement of a focus lens 4 arranged movably on the optical axis of the telescope.
The user is then able to identify a reticle 1, which is illuminated by means of an illumination device 3 via a beam splitter 2, and the mirror image of said reticle, said mirror image being reflected at the autocollimation target 6, in the image plane. In the ideal case where the autocollimation target 6 is aligned precisely perpendicularly with respect to the optical axis of the telescope, the reticle 1 and the mirror image thereof coincide, and no further measures are necessary.
FIG. 2 schematically reveals a case in which the autocorrelation target is not aligned precisely perpendicularly with respect to the optical axis of the telescope. Here, the user discerns a deviation between the reticle 1a and the mirror image 1b thereof, which deviation is dependent on the inclination and the orientation of the autocollimation target 6 and is illustrated by way of example in FIG. 3a. In order to correct the deviation, the user changes the horizontal angle and the vertical angle of the telescope until the reticle and the mirror image thereof coincide, as is illustrated in FIG. 3b. The inclination and the orientation of the autocollimation target are then determined from the horizontal and vertical angles of the telescope. FIG. 2 reveals a case in which a vertical inclination angle of the autocollimation target is α. A reflection angle at which the light beams 5 are reflected is accordingly 2×α. An illustration of the horizontal deviation in FIG. 2 has been dispensed with, for reasons of simplified illustration.
In order to cause the optical axis of the telescope to be incident on the autocollimation target perpendicularly, it is therefore necessary either to rotate the telescope by a in the vertical direction, or to rotate the autocollimation target by the angle α in the vertical direction. An analogous rotation of the telescope or of the autocollimation target in the horizontal direction then has the effect that the optical axis of the telescope is perpendicular to the autocollimation target.
FIG. 3a illustrates an incomplete reticle 1a. A reflection of the reticle 1 by a mirror fitted to the autocollimation target leads to a mirror image 1b of the reticle 1a. The adjustment of the telescope or of the autocollimation target as described in the previous paragraphs results in a displacement of the mirror image until the reticle 1a with precise, perpendicular alignment with the autocollimation target 6 together with its mirror image 1b produces the image of a complete reticle, as illustrated in FIG. 3b. 
There is a need for a telescope with which an autocollimation can be carried out automatically, and for a method for automatically carrying out an autocollimation.